I recently spoke at the Oxford Union in support of our nuclear deterrent. It was a timely debate as the issue risks becoming politically divisive just as we gear up to replace our four existing Vanguard Class nuclear submarines.

Thirty years ago, the leader of the opposition backed unilateral disarmament as we faced aggression from nuclear armed powers who did not share our values of democracy, freedom and the rule of law.

Today, the picture is depressingly similar. This weekend Jeremy Corbyn, the Labour leader will address a rally of the Campaign for Nuclear Disarmament.

My argument to him is the same as the one I made to the Oxford Union.

First, it is about realism. We all desire a world free from nuclear weapons. But unilateral disarmament does not mean a safer world.

We’ve reduced our nuclear forces by well over half since the height of the Cold War. By the mid-2020s, we’ll have reduced our stockpile to no more than 180 warheads.

Yet despite our honourable intentions, a resurgent Russia repeatedly rattles its nuclear sabre while North Korea already this year exploded a bomb and fired a ballistic missile in defiance of the international community.

And the dangers we’re facing are growing in complexity, diversity and scale. We can’t predict the threats of next week, let alone what will happen in the 2030s, the 2040s and the 2050s. Disarming now would be a reckless gamble with our national security that would play into the hands of our enemies.

My second point is that the deterrent works. It wasn’t designed to stop Daesh atrocities but to prevent nuclear blackmail and major war. Well, we haven’t had a major conflict in 70 years, nor has a single country under the nuclear umbrella been invaded.

Our operationally independent deterrent also strengthens NATO – giving it a second centre of decision-making to complicate an adversary’s calculations.

My third reason for maintaining our nuclear arsenal? TINA: there is no alternative. The Trident Alternatives Review in 2013 demonstrated no other system is as stable, assured to deliver, and as cost effective as the current four submarine solution.

What about part-time deterrents? Hiding our nuclear warheads in a bunker? Or submarines without weapons? Let’s get real. Our deterrent has to deter. Half-baked measures could be ruthlessly exploited by our adversaries.

As for future technologies detecting submarines, don’t hold your breath. Admiral Lord Boyce, former First Sea Lord and submarine commander, says we’re more likely to put a man on Mars within the next six months than make the seas transparent within the next 30 years. Such fears aren’t stopping the US and Russia spending billions upgrading their submarine fleets.

Naturally, Oxford’s smart students wondered about cost. Building four new submarines will come to around £31 billion. Yes, it’s a large sum of money.

But spread over 35 years and accounting for less than 0.2 per cent per year of total Government spending, I believe is an insurance premium worth paying. Those who want to scrap our nation’s ultimate security policy, must prove Britain is safer without it.

So what was the outcome of the debate? A resounding victory in favour of keeping our nuclear deterrent. The message was clear: put the case and you’ll win the argument.

So in the run up to the Parliamentary vote later this year, this Government will be getting behind Successor. In an unpredictable world, it’s the only way to guarantee our security and prosperity.